Aqueous systems for coating objects are gaining in importance because environmental protection conditions are becoming increasingly stringent. Their properties must be comparable with conventional systems, i.e. ones which contain solvents. Of the cold-curing coating compositions, water-dilutable epoxy resin systems have increasingly gained in importance. These two-component (2C) systems have excellent properties, such as good drying and rapid complete curing, very good adhesion to most substrates, very good inter-layer adhesion, good corrosion protection of metals.
Various aqueous epoxy/amine systems based on different binders have already been described. DE-A-36 43 751 for example describes specific epoxy compounds based on aromatic polyols. EP-A-000 605, EP-A-387 418 and DE-A-43 44 510 describe various amine hardeners for aqueous epoxy systems, based on aminourethanes or on specific epoxy/amine adducts for example. DE-A 41 23 860 quotes conventional aqueous epoxy/amine systems which additionally contain a non-ionic polyurethane resin.
The disadvantage of the known aqueous epoxy/amine systems is that coating compositions produced from them exhibit unsatisfactory sandability, particularly in the dry state. On the one hand the coatings obtained are so hard that when sanding, it is very time-consuming to achieve sufficient material removal and/or sanding is not possible at all. On the other hand there are aqueous epoxy/amine systems which soften quickly when being sanded because of their marked thermoplasticity and soon block up the sandpaper.